Efeito residual da adubação fosfatada e plantas de cobertura hibernais sob a produtividade de soja e milho

Abstract

Phosphorus is an essential nutrient for plant development and is present in high amounts in the vast majority of Brazilian soils, but the fraction readily available to plants represents a small portion of this amount. Based on this assumption, the present work aimed to evaluate the residual effect of different phosphate sources and the use of cover crops species on phosphorus solubilization. The experiment was implemented in 2009 in the experimental area of the Universidade Tecnológica Federal do Paraná (UTFPR), Dois Vizinhos Campus, located at a latitude of 25° 41' 34.05" S, longitude of 53° 5' 42.42" O and altitude of 526 meters. The experimental design is bifatorial (3x8), with 3 treatments of phosphate fertilizers, soluble (simple superphosphate), insoluble (natural phosphate) and without phosphorus application (control), associated with 7 species of winter cover crops: Vetch (Vicia sativa L. ), white lupin (Lupinus albus L.), forage turnip (Raphanus sativus L.), ryegrass (Lolium multiflorum Lam), black oat (Avena strigosa Schreb), rye (Secale cereale L.), a cover crop mix composed of turnip, oat and rye plus a plot that remains fallow during the winter (control). The experiment contained 24 treatments with 3 repetitions in randomized blocks, totaling 72 sampling units of 25 m² each (5 x 5 meters). Phosphate fertilizers were applied between 2009 and 2015 with an annual dosage of 100 kg ha-1 of P2O5. The variables analyzed were: dry mass of winter cover plants, grain yield and yield components of soybean and corn crops, evaluated in the 2019/2020 and 2020/2021 harvests, respectively. In the biomass production of the cover plants there was a highlight for the grasses in general, and the highest accumulations were obtained with the use of phosphorus sources, differing among themselves according to the plant species. For soybean, the responses among the P sources were not different, while in the treatments with absence of P the productive inferiority occurred especially in the fallow treatment. For corn, on the other hand, there were more considerable variations among the sources, differing statistically in some species of cover crops, with superiority for natural phosphate again. Therefore, the residual effect between the sources of phosphate had variations according to the species of cover crop, but in general the natural phosphate had the greatest response and ensured a productive support even after 5 years exploiting the residual effect present in the soil.